In present day fibre-pulp processing techniques, the pulp is thickened in a separate unit, for example a screw-press thickener, while refinement of the pulp is effected in a unit separate from the thickener, for example a disc refiner. Consequently, a screw feeder is required for transporting pulp from the pulp-thickening unit to the pulp-refining unit, this screw-feeder also serving as a refiner-infeed screw. In an arrangement such as this, the pulp is liable to absorb air during its passage from the outlet of the thickener to the inlet of the refiner, among other things due to the fact that the pressure created within the pulp in the screw-press thickening unit and the extent to which the pulp has been compressed therein cannot be maintained during transfer of the pulp by the feed screw. All air introduced into the pulp subsequent to it thickening has a deleterious effect on the subsequent treatment stages, however, and consequently the aforedescribed method of transferring pulp to the feed screw is encumbered with serious disadvantages.
Another disadvantage with present day apparatus arrangements of this kind, is that they require the provision of an additional unit, namely the combined conveying and infeed screw, which increases costs relating to initial investment, operation and maintenance.
In addition, each additional unit presents a stoppage hazard, and makes it difficult to sustain or reach a uniform pulp flow to the refiner. Another obvious disadvantage is that each additional unit requires a corresponding amount of space to be made available.
The prime object of the present invention is to provide an apparatus of the aforementioned kind intended for thickening, i.e. de-watering, and refining fibre-pulp suspensions, in which the aforementioned disadvantages are eliminated.
The general solution to the problem upon which the invention is based resides in the understanding that all the aforementioned disadvantages can be eliminated by connecting the screw-press thickener directly to the refiner, in the absence of an interconnecting combined pulp-conveying and infeed screw. In this way there is provided a fully closed system in which the pressure created in the pulp in the screw-press thickener and the extent to which the pulp is compressed therein can be maintained right up to the point at which the pulp is fed into the refiner. In this way problems related to the introduction of air into the pulp and the necessity of using a separate unit are eliminated.